Motorcycle riding is an activity that can be enjoyed by a wide variety of riders having different ages and skill levels. For many, the thrill and excitement of riding a motorcycle is unparalleled by any other activity. And motorcycle riding can be enjoyed by riders who lack the physical fitness and stamina required by many other forms of outdoor recreation.
Nevertheless, motorcycle riding does require some physical ability on the rider's part, especially when the motorcycle is standing still. While a motorcycle may be easy to balance and control while it is in motion, it can be very difficult to manage and even dangerous when stopped or nearly stopped. This can make it very difficult for some riders to operate a motorcycle, especially riders who are senior in age, physically impaired, short in stature, or who simply lack the required physical strength to hold a heavy motorcycle upright while stopping, dismounting, and deploying the kick-stand. As a result, many physically impaired riders, senior riders, women, and others must be content to ride a very light bike, or not to ride at all.
One approach for riders who have difficulty managing a standard motorcycle is to ride a three-wheeled motorcycle, sometimes referred to as a “trike,” which has been designed to stand on its own when stopped, thereby eliminating most or all difficulties associated with managing a stopped 2-wheel motorcycle. In some cases, a conventional 2-wheel motorcycle can be converted to a trike, thereby saving cost and providing a wider selection of models available for three-wheel riding.
However, a trike that has been designed to remain upright when standing still presents inherent problems while riding. Specifically, when turning it is desirable for a motorcycle to “bank” into the turn, i.e. to tilt or lean inward so as to counteract the centripetal turning force and maintain the rider's apparent center of gravity above the wheels. Banking during turns improves riding performance and safety, and is also one of the more enjoyable aspects of riding. However, if the two side-by-side parallel wheels of a trike are fixed in height relative to each other, then one of them will tend to lift off of the ground when the trike goes around a curve.
So as to mitigate this problem, some trikes provide a suspension that allows the trike to tilt during a turn without lifting a wheel. One approach is to mount the two parallel wheels on separate lever arms that pivot vertically so as to allow the wheels to separately move up and down when needed. Typically, control rods are connected to the lever arms, whereby the control rods control the vertical movements of the wheels. In some of these designs a “rocker arm” connects the two control rods to each other, thereby requiring that the wheels always move symmetrically in opposite directions. This approach effectively couples the wheel movements to each other, but is generally bulky and difficult to retro-fit to existing 2-wheel motorcycles.
Other lever arm designs use a pneumatic or hydraulic piston mounted on each control rod to manage the vertical movements of the wheels. In some of these designs the hydraulic reservoirs of the pistons are connected to each other, so that an upward movement of one of the wheels forces the other wheel downward. However, these designs do not always cope well when both wheels are lifted off of the ground, for example during servicing, since they can allow both of the parallel wheels to drop down simultaneously to the maximum extensions of the control rods.
In other pneumatic or hydraulic designs the control rods are managed by a processor that uses sensors to determine a speed, handlebar orientation, acceleration, frame orientation, and/or other status parameter of the vehicle, calculates an appropriate tilt angle, and then adjusts the pneumatic or hydraulic system accordingly. However, this approach can be complex, costly, and somewhat unnatural, since the tilt responds to a sensor-based calculation, rather than responding directly to the actual forces encountered by the trike while in operation.
Of course, if the trike is to stand upright on its own, either a conventional “kick-stand” must be provided, or the tilting suspension must provide some mechanism to lock the wheels in place when the trike is not in motion. In some mechanical designs, the suspension is simply locked in place when a manual control is actuated. However, this requires an extra step on the part of the rider. Other designs automatically adjust the suspension to hold the frame “vertical” when certain conditions are sensed, such as a low speed, a straight handlebar orientation, slippage of a wheel, or a sustained frame tilt. However, this approach can require a complex control and sensing system to avoid undesirable results, such as tilting the trike at an unsafe angle when on a hillside.
In addition to the issues described above, riding a “trike” can also carry with it a certain social stigma, so that a rider's enjoyment of riding a trike may be diminished by his or her concern regarding how he or she may be perceived by nearby riders of 2-wheel motorcycles.
What is needed, therefore, is a wheel suspension system for a three-wheeled motorcycle or “trike” that will allow the trike to bank naturally when turning but will hold the frame vertical when the trike is not in motion, is simple in design and yet responds appropriately to hills and roadway depressions, can be retrofitted to existing 2-wheel motorcycles, and can emulate the appearance of a 2-wheel motorcycle, so as to minimize any perceived stigma of riding a trike.